Our current understanding about the pathogenesis of osteoporosis is limited by a lack of information about the factors that determine the amount of bone gained during growth. Since the attainment of greater bone mass at skeletal maturity may reduce the risk of developing osteoporosis later in life, a better understanding of the determinants of bone density during growth in childhood and adolescence is required. Preliminary cross-sectional studies indicate that bone density increases dramatically during puberty both in boys and in girls and that the extent of this rise during late puberty is greater in blacks than in whites. However, the factors responsible for increases in bone density during adolescence and the mechanisms which account for the development of racial differences in bone mass at this time in life remain uncertain. Specifically, the role of alterations in the serum levels of several important modifiers of bone cell metabolism during puberty, such as sex steroids and calcium-regulating hormones is unknown; the possibility that variations in the response of bone at the tissue level to these important regulators of bone metabolism also wan-ants further investigation. It is the purpose of the current proposal to examine more closely the roles of sex steroids and calcium regulating hormones as determinants of the normal pubertal increase in bone density in growing black and white children. The following objectives are delineated: 1. To characterize the changes in vertebral bone density of cancellous and cortical bone density at each stage of sexual development in black and white males and females. 2 .To determine the relationship between increases in bone density during-puberty and the serum levels of sex steroids and calcium regulating hormones. 3 . To determine whether prepubertal measurements of vertebral bone density predict bone density at skeletal maturity. 4. To compare both the response of bone and the change in growth hormone secretion in black and white children after estrogen administration.